1. Field of the Invention
The present invention relates to a method for controlling an image forming apparatus, a program for controlling an image forming apparatus, and an image forming apparatus.
2. Description of the Related Art
An image forming apparatus, such as a digital copying machine or a multifunction (all-in-one) printer, has a function of scanning/reading a document and a function of recording document image data on a recording sheet.
For example, an image forming apparatus scans/reads a document and successively converts document image data into recording data. Then, the image forming apparatus transfers the recording data to a printer for printing. If the number of required copies is plural, the above-mentioned sequential processing of the image forming apparatus is repeated plural times for one document to be copied.
However, repeatedly executing a scan/read operation for each sheet takes a long time to accomplish the entire copy operation for the requested number of copies. To solve this problem, document image data read in a copy operation for the first sheet can be stored in an image memory while being recorded on the sheet by a printer. The printer can execute a succeeding copy operation for residual sheets based on the image data stored in the image memory.
For example, as discussed in Japanese Patent Application Laid-Open No. 11-331457, a copy operation for printing plural sheets from the same document includes sequential processes of scanning/reading a document, compressing read image data, storing compressed image data into an image memory, reading compressed image data from the image memory, expanding the compressed image data, and transferring the expanded image data to a printer. According to the above-mentioned copy operation, succeeding sheets can be speedily printed and a memory capacity of the image memory required for the processing can be relatively small.
However, a compression format of image data may not be effective for every image data characteristics. Therefore, expected data compression effects may not be obtained if the compression format does not match the characteristics of image data.
For example, when data compression/expansion processing is required for inputting/outputting image data to/from an image memory, compression effects may vary depending on the contents of a document. Computation resources used for compression/expansion processing may be useless.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 2003-087467, compressed image data may not be completely stored in an image memory depending on the contents of a document. In this case, a succeeding copy operation for residual sheets cannot be carried out. The requested copy operation for plural sheets ends in failure. As a result, the succeeding copy operation method is forcibly changed to a method including processes of repeatedly executing a scan/read operation for each sheet.
To improve the copy quality, a scanner with a higher resolution is required to scan/read a document and a printer with a higher resolution is required to record the document image. To this end, an image forming apparatus is equipped with a large-scale read buffer memory and a large-scale record buffer memory.
On the other hand, due to a wide-spread use of digital copying machines and multifunction (all-in-one) printers, the cost of each machine has been decreasing. The capacity of a memory installable on each machine is limited to a lower capacity and expected to realize advanced functions.
In other words, a limited memory capacity is shared by an image memory, a read buffer memory, and a record buffer memory. In particular, the image memory stores compressed image data. If an available memory capacity is small, securing a sufficient capacity for the image memory may be difficult.
For example, in a copy operation for plural sheets, a memory capacity available for an image memory tends to become smaller. Thus, compressed image data for one page may not be completely stored in the image memory.
According to the above-mentioned conventional arrangement, if a memory overflow occurs in a first copy operation, the succeeding copy operation for residual sheets is stopped or performed by repeatedly executing a scan/read operation for each sheet with a decreased throughput.